Pulpstone joint material



Aug. 3, 1948. Y. H. NoRDsTRoM 2,446,513

PULPs'roNE JOINT MATERIAL Filed Sept. 30, 1947 4 i u invento-r' i Vngve H. Nordstmn( L Ht torn-ey Patented Aug.. 3, 1948 PULPSTON E JOINT MATERIAL Yngve H. Nordstrom, Worcester, Mass., asslgnor to Norton Company, Worcester, Mass., a corporation of Massachusetts Application September 30, 1947, Serial No. 776,931

4 Claims. (Cl. 5l-206.4)

The invention relates to joint material for pulpstones and to the combination of pulpstone blocks and center with such joint material.

One object of the invention is to reduce groovlng of pulpstones. Another object o'f the invention is to provide a pulpstone joint material which is highly adhesive. Another object of the invention is to provide a pulpstone joint material which is readily compressible under the forces developed in grinding and the compressibility of which may Aloe readily controlled. .Another object of the invention is to provide a pulpstone jolntmaterial which is resistant to hot pulp water. Another object of the invention is to provide a joint material which will prevent breaking down of the edges ofthe pulpstone blocks. Another object of the invention is to provide a joint material having one or more of the above characteristics which may be readily applied to faces of the blocks to facilitate rapid construction of an assembly of blocks for the manufacture of a stone. Another object is to provide a material which will readily ow at vulcanizing temperatures thus to lll all pores and any irregularities in the surfaces of the blocks. Another object is to provide a material of the character indicated which will not deteriorate with age. 'Another object of the invention is to provide an improvement in the pulpstonel joint material described and claimed in U. S. Letters Patent to Larsson No, 2,054,771 of September 15, 1936 (therein termed a li'lller). Another object of the invention is to provide a pulpstone joint which is strongly attached to the blocks so that when the blocks pullapart .no gap will be formed.

Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts, and in the several steps and relation and order of each of'said steps to one or more of the others thereof, all as will be illustratively described herein and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings illustrating one of many possible embodiments of the mechanical features of this invention,

Figure 1 is a fragmentary sectional view of a pulpstone having joint material according` to the invention,

Figure 2 is an elevation on an enlarged scale of a holding bolt for attaching the blocks to the pulpstone center, and f Figure 3 is an exploded view on a greatly enlarged scale showing sections of fragments of called segments, to form an exterior cylindrical surface, clamping the blocks together in such arrangement, locating a mould sleeve or the like inside of the blocks and then pouring concrete between the blocks and the mould sleeve to form the center. The hole leftby the mould sleeve is the mounting hole for the pulpstbne or in some cases the sleevey around which the concrete is moulded may remain as part of the pulpstone. Pulpstones of this general type are disclosed in U. S. Letters Patent to J eppson No. 2,032,484 of March 3, 1936, U. S. Letters Patent to Larsson No. 2,074,114 of March 16, 1937, U. S. Letters Patent to Larsson No. 2,141,608 of December 27, 1938, U. S. Letters Patent to Howe and Washburn No; 2,421,885 of June 10, 1947 and U. S. Letters Patent to Howe and Washburn No. 2,421,886 of June 10, 1947. In these patents and elsewhere there has been disclosed the manner of assembling the abrasive blocks separating them with sheets of Joint material, clamping the blocks together, placing the mould sleeve in position and locating a steel cage made of ser-ies of concentric hoops .between the blocks and the mould sleeve and pouring concrete to form the pulpstone center and, after the concrete has set, heating Ithe entire assembly to bake or vulcanize the joint material. The present invention is concerned with such joint material which is an improvement over` :that disclosed in U. S. letters Patent to Larsson 2,054,771 and to the combination of pulpstone blocks and cen-ters with such joint material.

Referring now to the drawing-s I prov-ide pulpstone blocks I0 and a concrete center Il. 'blocks I0 may be held to the center M by means of bolts of which the bolts i2 are illustrative. Many different constructions will be found in the patents above listed and I may use any of such constructions or others including improvements such as disclosed in an application of Jeppson and Howe, Serial No. 770,888, filed August 27, 1947.

The construction illustrated herein is taken from the Patent 2,421,885 to Howe and Washburn. However, a slight modication of the holding bolts I2 i herein illustrated but well within the disclos re in the Howe and Washburn patent. This particular illustrative embodiment of a pulpstone therefor includes cages I5 formed from steel hoops."

'I'hepu'lpstone joint material 20 is located in ra- 3 dial axial planes be'tween the blocks and also in angular planes between other faces of the blocks which may have various shapes as seen in plan, a common shape being a six sided figure formed by joining two identical trapezoids on their long bases.

Referring now to Fig. 3 which illustrates the joinder of any two blocks I with the Joint material 20, I first preferably paint the faces of the abrasive blocks I0 to be joined with a layer of phenolic resin, furfurai and quartz filler 2|. The phenolic resin may be solid reactable phenol formaldehyde resin containing hexamethylene tetramine and including a small percentage of cresci formaldehyde such as is sold under the designation BR 2417. The quartz filler should be 'fine quartz sand for example about grit size 300.

I may use in the neighborhood of 70 percent by weight on the entire mix of quartz sand. Enough furfural is added to dissolve the uncured resin BR 2417 sufficiently to make a heavy paste of the mixture. This heavy paste forms the layers 2| and penetrates the pores and cavities of the faces of the abrasive blocks l0. The paste may be applied with an ordinary heavy paint brush. Whenheated to polymerizing or vulcanizing temperature (much the same and in this case the temperature of about 146 C. can be used) for a number of hours, the layer 2| becomes a strong, hard layer of cured phenolic resin with a quartz filler and adheres well to the blocks I0 and also to the joint material 20 which will now be described.

Figure 3 shows the joint material 20 between fragments of two blocks lll which have layers 2|. However, as soon as the layers 2| have been painted onto the blocks I0 the latter will be pushed together so that the layers 2| will be in firm contact with the joint material 20. In other words in the construction of a pulpstone as described in any of the patents above listed the blocks I0 are painted with the layers 2|, pieces of joint material are then placed in position and the blocks are brought together to build up the pulpstone. Therefore the pulpstone builder has, besides a great number of blocks I0 and a quantity of paste material to form the layers 2|, a pile of joints 20 cut to size and he then proceeds to build the pulpstone much as a mason builds a brick wall. I

The joint material 20 is a sandwich. It comprises outer layers 22 and an inner layer 23. I will now give an illustrative formula for the outer layers 2.2.

Example 1 Parts by Material Weight sess To the above, if desired, may be added 60 percent by weight on the entire layer of abrasive material for example fused alumina abrasive grit size 150. E

'Ihe inner layer 23 is based upon natural rubber. The following is an example for the inner layer.

The sandwiches 20 at the time when the pulpstone is being built are uncured, that is to say, the outer layers 22 and the inner layer 23 are unvulcanized. The material, however, especially the outer layers 22, is tacky enough so that the sandwiches can be readily handled without falling to pieces. The material is also soft enough so that it can be readily cut into the desired shapes.

After the blocks i0 have been put together with the joint material 20 between faces of blocks, the rings oi blocks are securely clamped by heavy hoop shaped clamps having radial screws which are screwed inwardly to exert a strong pressure against the blocks to hold them in firm engagement with the joint material 20 all as described in the patents above listed. The assembly is then taken to a large vulcanizing oven and heat treated for about fifteen hours at a temperature of 146 C. This vulcanizes the layers 22 and 23 of the sandwich joint material 20 and polymerizes the phenolic layers 2| and the blocks I0 are thereby firmly cemented together. Thereafter follows the operation of pouring concrete as described in the patents and it is the holding bolts I2 or other means which are relied upon to the hold the blocks to the concrete center II, but the adhesion of the joint material 20 to the blocks I0 is important to keep the joint material in place and to protect the edges 0f the blocks. above described, excellent adhesion is secured.

A feature of the invention is the use of an inner layer 23 based on natural rubber with outer layers 22 based on butadiene-acrylic nitrile copolymer. It is desired that the outer layers 22 be hard in order to protect the edges of the blocks Il! during grinding. It is desired that the inner layer 23 be not quite so hard but `compressible in order that when the blocks i0 expand due to the heat of grinding they shall not be shattered by cornpressive forces. The use of a single mixture for the joint material 20 has been found to have certain disadvantages. If too hard it will not flow readily enough and hence, even though having cork granules therein, may not be compressible enough to protect the blocks |0 when they expand. On the other hand, if such joint material 20 is too soft it wears away rapidly and thus forms grooves in the surface of the pulpstone and when the grooves have formed the edges of the blocks I0 `rapidly wear away. Therefore, in the manufacture of pulpstones using the joint material described in patent to Larsson 2,054,771 a compromise was achieved in which the joint material was neither too hard nor too soft and good results were obtained, but by using the sandwich joints described herein the compromise is no longer needed and still better results can be achieved.

Another feature of the invention is that the joint material 20 is strongly united to the blocks l0 by the phenolic layers 2l. If heating of the periphery of the pulpstone causes surfaces of adjacent blocks to move toward each other, naturally subsequent cooling causes them to move away from each other. Furthermore, pulpstones are sometimes run continuously for a week and By the use of the combination as` by that time the concrete core Il will be hot. Then, if the stone is unused for some time, the

periphery will cool first and this creates a condition where the faces of the blocks are farther apart than normally. A feature of the invention is that the sandwich joint material 2i) is expansible as Well as firmly attached to the blocks. This prevents the creation of any gaps in the joint material or between it and the block. With the use of previous materials such gaps were often found and they constitute a danger to the pulpstone causing fracture of the edges of the blocks.

Another feature of the invention is that the joint material taken as'a whole is of just about the right hardness so that grooves in the surface of the pulpstone are not formed at the joints. Grooving is undesirable because it frequently results in fracture of the edge of the blocks.

It might be thought that the layers 22 and 23 could all be based upon natural rubber'or could al1 be based upon a synthetic rubber only having different amounts of sulphur therein to achieve diierent hardness. It has been found, however, that the sulphur migrates to such an extent during the vulcanization that substantially a one material joint results even though the material be initially formed in three layers having different amounts of sulphur. However, since the same percentage of sulphurproduces a harder butadiene-acrylic nitrile copolymer than it does a natural rubber I am enabled, by the combination of this invention, to achieve a vulcanized sandwich joint wherein the outer layers 22 are harder than the inner layer 23. It will be noticed that I deliberately place less sulphur in the inner layer 23 than in the louter layers 22 and although the sulphur does to a considerable extent migrate, nevertheless the result of different hardness is obtained. Furthermore, I believe that there is less migration of the sulphur from the butadieneacrylic nitrile layers 22 to the rubber layer 23 than there would be if both layers were of either one or the other material. With regard to other synthetic rubbers for either of the layers, such as butadiene-styrene, I do not believe they will give the results.

With regard to the various ingredients for the layers 22 and 23, I will now give the reason and purpose for each ingredient so far as it is known to me. Commencing with the outer layers 22, the butadiene-acrylic nitrile is, as stated, the

basic ingredient which is to form the copolymer..

Various grades of this polymerizable mixture can be used. The gas carbon black is a filler and promotes workability on the calendar rolls. The sulphur is of course the vulcanizing agent. The comarone-indene resin promotes plasticity of the uncured mix and permits the sandwich 20 to conform to irregularities of the blocks i0. The pente, erythritol formal is both a cross linking vulcanizing agent and a plasticizer. Theineterogeneous mixture of alkylated benzene with a small percentage of a heterogeneous mixture of alkylated naphthalene is a plasticize'r and promotes ta-ckiness. The poly vinylidene dichloride is a catalyzer to cause the penta erythritol formal to cross link during the vulcanizing.

With regard to the inner layer 23, the rubber in theform of smoked sheet is, as stated, the basic ingredient. The gas carbon black is a lle'r as in the case of the outer layers 22 and the sulphur is the vulcanizing agent. The diazo amino benzene functions to liberate nitrogen during the curing and this makes the inner layer 23 porous and spongy. The liberation of this nitroset forth is to be interpreted as illustrative and not Een gas produces very fine pores and the walls of which are all rubber so the material is quite strong but at the same time can readily be compressed. It should be understood that rubber without pores may-be deformable but it is not to any great extent compressible and a large sheet of rubber which has been vulcanized to medium hard rubber is not sufliciently deformable to savethe blocks I0 from cracking when they expand. By making the layer 23 porous, however, it can be compressed thus protecting the pulpstone from the forces of expansion due to heating. I may use other agents to liberate gas. For example, a 'combination of sodium bicarbonate and stearic acid to the extent of about ten parts of the former and five parts of the latter Ion the above formula for the inner layer 23 has been found tov be satisfactory. Other gas forming agents which will not detrimentally affect the rubber can be used. It is desirable that the gas start to format about C. so that the porosity will commence before the rubber has been vulcanized. Both of the agents mentioned wil-l give off gas at or about 100f7 C. but not much below that temperature.

The use of abrasive in the outer layers 22 is optional. However` the use of the abrasive makes it easier to sheet out material on the mill rolls.

The layers 22 are vulcanized both by the sulphur and the penta erythritol formal. Various degrees of hardness of these layers 22 are useful in this invention provided that these layers are at least as hard as is obtained by vulcanizingat 146 C. for fifteen hours with 25 percent on the copolymer per se of sulphur. Various degrees of hardness of the layer 23 are useful in this invention provided that this layer is no harder than is obtainedby vulcanizing at 146 C. for fifteen hours with 30 percent on the rubber per se of sulphur and no softer than is obtained by vulcanizing at 146 C. for fifteen hours with 12 percent on the' rubber per se of sulphur. In connection with the above it is pointed out that the copolymer vulcanized at the temperature and for the period mentioned with 25 percent of sulphur is harder than the natural rubber vulcanized at the temperature and f or the period mentioned with 30 percent of sulphur.

The compressibility of the inner layer 23 can be varied by changing the thickness thereof. It can also be varied by varying the quantity of diazo amino benzene or other gas producing agent. The outer layers 22 can be of varying thickness. Useful results according to this inventionv can be obtained if the outer layers 22 are from .025" to .100" thick and the inner layer 23 is from .025" to .200 thick. Also the amount of diazo amino benzene can be varied from one percent to ten percent on the rubberper se.

It will thus be seen that there has been provided by this invention a joint material for pulpstones and the combination of pulpstone blocks and center with such joint material in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodimentsmight be made ofthe mechanical featuresv of the above invention and as the compositions herein described might be varied in various parts all without departing from the scope of the invention, it is to be understood that all matter -hereinbefore in a limiting sense.

I claim: 1. A pulpstone joint filler consisting of a sandwich having outer layers of butadieneacrylic nitrile copolymer vulcanized to a condition at least as hard as is obtained by vulcaniing at 146 C. for 15 hours with 25% on the copolymer per se of sulphur, and an inner layer of natural rubber vulcanized to a hardness no harder than is obtained by vulcanizing at 146 C. for 15 hours with 30% on the rubber per se of sulphur and no softer than is obtained by vulcanizing at 146 C. for hours with 12% on the rubber per se of sulphur, said outer layers having a thickness of from .025" to .100" and said inner layer having a thickness of from .025" to .200", said inner layer having a porosity produced by the generation of gas during the vulcanization.

2. A pulpstone joint ller consisting of a sandwich having outer layers of butadiene-acrylic nitrile copolymer vulcanized to a condition at least as hard as is obtained by vulcanizing at 146 C. for 15 hours with 25% on the copolymer per se of sulphur, and an inner layer of natural rubber vulcanized to a hardness no harder than is obtained by'vulcanlzing at 146 C. for 15 hours with 30% on the rubber per se of sulphur and no softer than is obtained by vulcanizing at 146 C. for 15 hours with 12% on the rubber per se of sulphur, said inner layer having a porosity produced by the generation of gas during the vulcanization.

3. A pulpstone comprising a plurality of blocks of vitriiied bonded abrasive material arranged to form an outer surface of revolution, a concrete center inside of and in contact with said blocks, said blocks being secured to said concrete center, and joint illiers between adjacent faces of said blocks each consisting of a sandwich having outer layers o! butadiene-acrylic nitrile copolymer vulcanized to a condition at least as hard as is obtained by vulcanizing at 146 C. for 15 hours with 25% on the polymer per se of sulphur, and an inner layer of natural rubber vulcanized toa hardness no harder than is obtained by vulcanizing at 146 C. for 15 hours with 30% on the rubber per se of sulphur and no softer than is obtained by vulcanizing at 146 C. for 15 hours with 12% on the rubber per se of sulphur, said outer layers having a thickness of from .025" to .100" and said inner layer having a thickness of from .025 to .200l said inner layer having a porosity produced by the generation of gas during the vulcanization.

4. A pulpstone comprising a plurality of blocks of vitrified bonded abrasive material arranged to form an outer surface of revolution, a concrete center inside of and in contact with said blocks, said blocks being secured to said concrete center, and Joint fillers between adjacent faces of said blocks each consisting of a sandwich having outer layers of butadiene-acrylic nitrile copolymer vulcanized to a condition at least as hard as is obtained by vulcanizing at 146 C. for 15 hours with 25% on the copolymer per se of sulphur, and an inner layer of natural rubber vulcanized to a hardness no harder than is obtained by vulcanizing at 146 C. for 15 hours with 30% on the rubber per se of sulphur and no softer than is obtained by vulcanizing at 146 C. for l5 hours with 12% on the rubber per se oi sulphur, said inner layer having a porosity produced by the generation of gas during the vulcanization. v

YNGVE H. NORDSTROM. 

